I. Field of Invention
This invention relates generally to electro-medical apparatus and more specifically to a transcutaneous electrical nerve stimulator which may be used to inhibit the transmission of pain impulses from the peripheral to the central nervous system.
II. Description of Prior Art
It is well known that the application of electrical stimulation to the body of a patient in the area of soreness or pain can have a therapeutic and anesthetizing effect, although the physiological basis is not completely understood. As is set forth in the Limoge U.S. Pat. No. 3,835,833, the application of electrical signals at electrodes placed at suitably chosen points on the body of a patient is capable of causing various therapeutic effects such as local anesthesia or relaxation of muscles and nerves. There are described in the prior art various electronic circuits for selectively applying electrical impulses of variable amplitude, frequency and duration. It is also recognized that the application of electrical stimulation can be accompanied by discomforting sensation such as a burning sensation, stinging or prickling. Further, it is known that the ability of a nerve cell to respond to a stimulus of given current magnitude is related to the duration of time during which the current impulse flows. This is often expressed graphically as a "Strength-Duration Curve". Thus, a reduction in time duration may be compensated for by an increase in current amplitude.